Advanced Transient Response Tests

In these tests we monitor the response of the PSU in two different scenarios. First a transient load (11A at +12V, 5A at 5V, 6A at 3.3V and 0.5A at 5VSB) is applied for 50 ms to the PSU, while the latter is working at a 20% load state. In the second scenario the PSU, while working with 50% load, is hit by the same transient load. In both tests, we measure the voltage drops that the transient load causes, using our oscilloscope. In any case voltages should remain within the regulation limits specified by the ATX specification. We must stress here, that the above tests are crucial, since they simulate transient loads that a PSU is very likely to handle (e.g. starting of a RAID array, an instant 100% load of CPU/VGAs etc.) We call these tests “Advanced Transient Response Tests” and they are designed to be very tough to master, especially for PSUs with capacities lower than 500W.





Judging from our previous tests, we expected much higher voltage drops on these tests, but the small Akasa proved us wrong. The +12V rail registered decent results and managed to keep the deviation close to 2.5% in the worst case scenario. Meanwhile the minor rails stayed below 4% and finally 5VSB performed quite well although at normal tests deviation on this rail was way too high. All in all the performance of the small Venom PSU at these, very demanding, tests was a pleasant surprise for us.

Below you will find the oscilloscope screenshots that we took during Advanced Transient Response Testing.

Transient Response at 20% Load

Transient Response at 50% Load

Turn-On Transient Tests

In the next set of tests we measure the response of the PSU in simpler scenarios of transient loads, during the turn on phase of the PSU. In the first test we turn off the PSU, dial 2A load at 5VSB and then switch on the PSU. In the second test, while the PSU is in standby, we dial the maximum load that +12V can handle and we start the PSU. In the last test, while the PSU is completely switched off (we cut off power or switch off the PSU's On/Off switch), we dial the maximum load that +12V can handle and then we switch on the PSU from the loader and we restore power. The ATX specification states that recorded spikes on all rails should not exceed 10% of their nominal values (e.g. +10% for 12V is 13.2V and for 5V is 5.5V).


A large spike registered at 5VSB during these tests. Thankfully it is below the 5.5V limit although at 5.3V you can't call it low. In the second test the +12V rail needs quite some time to settle down to normal levels. At least in this case no voltage overshoots were recorded by our scope. Finally in the third test the PSU registered the best performance during this test session since voltage settled down normally and there were no voltage overshoots. All in all the unit's performance in the first two tests spoil the picture here and inevitably some performance points are lost.